Electrical transformer



Patented Aug. 15, 1950 ELECTRICAL 'rasnsroamm John H. Chiles, Jr.,Sharon, Pa}, and Homer 0.

Hood, Brookfield, Ohio, ass znors to Westinghouse Electric Corporation,East Pittsburgh. Pa., a corporation of Pennsylvania Application May 28,1947, Serial No. 150,948

Claims. (Cl. 171-119) Our invention relates to electrical transform- Kers. In certain types of transformers, such as are suitable for use incertain types of protective systems for operating relays for theprotection of transmission lines in the event of a transmission linefault, the current from the transformer secondary winding for operatingthe pro- I tective relay flows upon an unbalance in the current flowingin the two halves of a, primary winding, having its midpoint grounded.Such a system is disclosed in U. S. Patent No. 2,183,646 to E. L. Harderfor Relaying Apparatus, issued December 19, 1939, and assigned to thesame assignee as this application. Such transformers are shown in theHarder patent as insulating transformers located at the opposite ends'ofthe pilot-wires connecting tripping relay stations located at differentpoints along the transmission line to be protected. In such insulatingtransformers it is desirable that substantially no current will flow inthe secondary circuit of the transformers when the voltage between eachprimary winding terminal to the grounded midpoint of the winding arealike.

It has been customary in transformers of this type to closely couple thetwo halves of the primary winding by winding two conductors togetherside-by-side so that the conductors are closely coupled throughout theentire winding lengths. One of these two conductors is used as one ofthe two primary winding coils, and the other, as the other primarywinding coil, constituting the two halves of the primary winding.

The insulation between the two halves of the primary winding is thenonly the conductor insulation, which is not altogether satisfactory,since the voltage between adjacent conductors may, under certainconditions, become quite large and cause failure of the transformerinsulation. 0n the other hand, if the two halves of the primary windingare separated mechanically, it is very difiicult to assemble them sothat the two halves will'be sufficiently symmetrical in their couplingto the secondary winding to provide It is a more specific object ofthe-invention to provide a transformer of the above-indicated characterhaving magnetic shields between the primary and secondary windings forso guiding the primary leakage flux as to prevent or greatly reduce theamount of this leakagefiux that links turns of the secondary winding.

Other objects and advantages of the invention will be apparent from thefollowing description of certain preferred embodiments of the invention,reference being had to the accompanying drawing,inwhich:

Figure l is an elevational view, partly in section, of a conventionaltransformer core and coil assembly; Fig. 2 is an elevational view, partyin section, of a transformer core and coil assembly arranged inaccordance with one preferred embodiment of the invention; I

Fig. 3 is a, diagram illustrating the connections of the primary andsecondary circuits of the transformer core and coil assembliesillustrated inFigs. l and 2;

Fig. 4 is an elevational view, partly in section, of a core and coilassembly arranged in accordance with another preferred embodiment of theinvention;

Fig. 5 is an elevational view, partly in section, of a core and coilassembly arranged in accordance with still another preferred embodimentof the invention, and

Fig. 6 is a diagram illustrating the connections of the primary andsecondary windings of the embodiments of the invention illustrated inFigsand 5.

Referring to the drawing and, particularly, to Figs. 1, 2 and 3 thereof,a transformer core structure 1 formed of magnetic material is provided,including a winding leg 2 and two outer legs 3 and 4, respectively,connected together at their upper and lower ends by the yoke portions 5and 6, respectively. The core structure provides two rectangular windows1 and 8 on opposite sides of the winding leg 2 through which thewindings are positioned about the winding leg 2. The primary winding llcomprises two similar coils or half windings l2 and I3, having theirouter terminal conductors l4 and I5 connected to the primary circuit ofthe transformer and their inner terminal conductors I 6 and I1 connectedtogether and through a common conductor [8 to ground at l9, as shown inFig. 3. The secondary winding 2| is shown about the winding leg 2 withinthe primary winding ll and is provided with terminal conductors 22 3 a..i 23 connected to the secondary winding circuit. The two primarywinding coils l2 and II are similar in construction and extend about,difierent portions of the winding leg 2, while the secondary winding 2!extends about the winding leg 2 over the portions thereof surrounded byboth primary winding coils l2 and It. The structure shown in Fig. 1 is aconventional prior art structure. If the two primary coils l2 and I3 arepositioned end-to-end (as shown), either-over or inside of the secondarywinding 2|, and are perfectly centered with respect to the winding legof the core and to the secondary winding, each primary coil willneutralize the effect of the other on the secondary winding when equalcurrents are flowing between each primary terminal through the twoprimary winding coils to ground. This condition is very diflicult toobtainin commercial production. It the two primary coils and thesecondary are not exactly symmetrical, certain current will flow in thesecondary due to this lack of symmetry, which is undesirable, since thesecondary current which is intended to flow upon unbalance between thetwo primary'coils for operating the protective relay will then beindeterminate in value and may cause operation of the relay underconditions not intended.

The major portion of the magnetic flux produced by the flow of currentin the primary coils i2 and I3 flows through the winding leg 2 andthrough a magnetic circuit including either the outer leg 3 or the outerleg 4, thus completing a magnetic circuit path within the core. Acertain portion of flux, primary leakage flux, will flow about theprimary winding coils l2 and i3 along lines represented generally by thedotted lines.

24 and 25 which will, to a greater or lesser extent, cut the windingturns of the secondary winding 2i. If the leakage flux from the coil i2and the leakage fiux from the coil i3 are equal and opposite indirection in the winding turns of the secondary winding 2|, their eflectwill be neutralized, and this is the desired condition. As aboveexplained, this condition is difficult to maintain in practice.

In accordance with one embodiment of the invention shown in Fig. 2,magnetic shields 26 and 21, comprising a plurality of layers of magventor greatly reduce the primary leakage flux linking with the turns of thesecondary winding, since the leakage flux will pass between the primarywinding coils and the secondary winding following the lower reluctancepath through the shield and back to the core, without linking thesecondary winding turns, as shown by the dotted line paths 24 and 25 inFig. 2.

In accordance with the embodiment of the invention illustrated in Fig.4, both the primary winding and the secondary winding are formed in twocoils or two half portions assembled endto-end about the winding leg 2of the core structure. The primary winding coils may be placed eitherinside or outside of the secondary winding coils and are connected inseries circuit relation with respect to each other with the connectionbetween them grounded ati |9,,as shown in with'respect to the structureillustrated in Figs. 1 and 2.

The secondary coils 3| and 32, which together comprise the secondarywinding, extend about portions of the winding leg 2 corresponding to thewinding leg surrounded by the primary winding coils l2 and I3,respectively. As shown in Figs. 4 and 5, the terminal conductors 33 and34 of the secondary coil 3| and the terminal conductors 35 and 36 of thesecondary winding coil 32 are connected, respectively, to junctionpoints 31 and 38 that in turn ar connected to the secondary circuitconductors 22 and 23, respectively, thus connecting the secondary coils3| and 32 in parallel circuit relation with respect to each other.

.a corresponding descrease in the voltage appearing across the secondarycoils when applied tothe secondary circuit conductors 22 and 23,reducing this voltage to a negligible value.

In the embodiment of the invention illustrated in Fig. 5, the circuitarrangements of the primary and secondary windings corresponds to thatshown in Figs. 4 and 6. Magnetic shields 6i and 42 corresponding tothose shown in Fig. 2

have been added and positioned between the primary and secondary windingcoils to provide equal air gaps at 23 and 29 between their opposite endsand the adjacent yoke portions 5 and 6, respectively, of the corestructure. The arrangement of the magnetic shields shown in Fig. 5,together with the parallel connected secondary coils, gives even betterresults than either the structural arrangements shown in either Fig. 2or 4 in that it combines the efl'ect of the magnetic shields in reducingthe primary leakage flux thatcuts the windings of the secondary circuitconductors with the use of the circulating current in the two secondarycoils resulting from any remaining primary leakage flux cutting thesecondary coils to further reduce the eiiectiveness of this flux by theflow of circulating current in the local circuit including the twosecondary coils 3| and 32.

It will be apparent from the above description of the invention thatmodifications may be made in the circuits and apparatus illustratedwithout departing from the spirit of the invention, and

we do not wish to be limited otherwise than by the scope of the appendedclaims.

We claim as our invention:

1. In a transformer, in combination, a core structure of magneticmaterial comprising a winding leg portion and two outer leg portions,and yoke portions connecting the corresponding ends of the three legportions together to form two continuous magnetic circuit paths for theflow of magnetic flux from the winding leg, a low-voltage winding aboutthe winding leg and a high-voltage winding about the low-voltagewinding, the high-voltage winding comprising two similar coils eachextending along substantially half of the length of the winding leg, thetwo coils being connected together and to ground at their Fisn e a manns Shown in 8- 3 76 adjacent ends and to the circuit conductors of acommon circuit at the ends remote from each other, and means formaintaining the effective coupling between one half of the high-voltagewinding and the low-voltage winding susbtantially the same as theeffective coupling between the other half of the high-voltage windingand the lowvoltage winding comprising magnetic material extendingbetween the high-voltage and lowvoltage windings to completely shieldthe lowvoltage winding and reduce the primary leakage magnetic fiuxlinking the low-voltage winding, said magnetic shield having similar airgaps at its opposite ends.

2. In a transformer, in combination, a core structure of magneticmaterial comprising a winding leg portion, two outer leg portions, andyoke portions connecting the corresponding ends of the leg portions toform two core windows on opposite sides of the winding leg, 9, primarywinding and a secondary extcnding through the core windows about thewinding leg of the core, each winding comprising two similiar coilspositioned end-to-end about different portions of the winding leg, eachone of the primary winding coils and a corresponding one of thesecondary winding coils being of the same length and positioned about acorresponding portion of the winding leg,

the two coils constituting the primary winding being connected in seriescircuit relation and the two coils constituting the secondary windingbeing connected in parallel circuit relation, and means for preventingor greatly reducing the primary leakage magnetic flux linking thesecondary winding turns, comprising a shield of magnetic materialextending between the primary and secondary windings, the ends of theshield being spaced from the yoke portions of the core to providesimilar air gaps between the opposite ends of the shield and theadjacent yoke portions.

3. In a transformer, in combination, a core structure of magneticmaterial comprising a winding leg portion and an outer leg portion, andyoke portions connecting the corresponding ends of the leg portionstogether to form a continuous magnetic circuit path for the flow ofmagnetic flux from the winding leg, a low-voltage winding and ahigh-voltage winding about the winding leg, the high-voltage windingcomprising two similar coils each extending along substantially half ofthe length of the winding leg, the two coils being connected togetherand to ground at their adjacent ends and to the circuit conductors of acommon circuit at the ends remote from each other, and means formaintaining the effective coupling between one half of the high-voltagewinding and the low-voltage winding substantially the same as theefiective coupling between the other half of the high-voltagewinding-and the low-voltage winding comprising magnetic materialextending between the high-voltage and lowvoltage windings to completelyshield the lowvoltage winding and reduce the primary leakage magneticflux linking the low-voltage winding, said magnetic shield havingsimilar air gaps at its opposite ends.

4. In a transformer, in combination, a core structure of magneticmaterial comprising a winding leg portion and two outer leg portions andyoke portions connecting the corresponding ends of the three legportions together to form two continuous magnetic circuit paths for theflow of magnetic flux from the winding leg, 9. lowvoltage winding and ahigh-voltage winding about the winding leg, the high-voltage windingcomprising two similar coils each extending along substantially half ofthe length of the winding leg, the two coils being connected togetherand to ground at their adjacent ends and to the circuit conductors of acommon circuit at the ends remote from each other, and means formaintaining the efiective coupling between one half of the high-voltagewinding and the low-voltage winding substantially the same as theeffective coupling between the other half of the high-voltage windingand the low-voltage winding comprising magnetic material extendingbetween the highvoltage and low-voltage windings to completely shieldthe low-voltage winding and reduce the primary leakage magnetic fluxlinking the lowvoltage winding, said magnetic shield having sim-' ilarair gaps at its opposite ends.

5. In a transformer, in combination, a core structure of magneticmaterial comprising a winding leg portion and an outer leg portion, andyoke portions connecting the corresponding ends of the leg portions toform a core window, a primary winding and a secondary winding extendingthrough the core window about the winding leg of the core, each windingcomprising two similar coils positioned endto-end about differentportions of the winding leg, each one of the primary winding coils and acorresponding one of the secondary winding coils being of the samelength and positioned about a corresponding portion of the winding leg,the two coils constituting the primary winding being connected in seriescircuit relation and the two coils constituting the secondary windingbeing connected in parallel circuit relation, and means for preventingor greatly reducing the primary leakage magnetic flux linking thesecondary winding turns, comprising a shield of magnetic materialextending between the primary and secondary windings, the ends of theshield being spaced from the yoke portions of the core to providesimilar air gaps between the opposite ends of the shield and theadjacent yoke portions.

JOHN CHIIES, JR. HOMER C. HOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS neuter Apr. 8, 1933

